I am "redoing" an old bungalow that is up on piers and is located in West Central Florida. There was no insulation between the floor joists, and I am wondering what is the best type to use in a Florida bungalow. I have replaced a bunch of the joists, and they are now on 16" centers. I have not yet put down my 3/4" plywood sub flooring. I would like to use 2" rigid foam insuation and fit it in before the plywood goes down. Does anyone know if this is a viable and effective insulation for this application? Batt insulation will be attacked by insects and rodents. The house is well shaded and stays cool, but I want to do it right while I have the opportunity. Any and all help is greatly appreciated!

Welcome to the Froum, Streamin:
Yes, 2" foam board would be adequate insulation in your area.A good tight fit and some adhesive would make it hang in there just fine. A word of caution though, most construction adhesives will dissolve foam board. There is a company named Con-Tech that makes an adhesive especially for foam board.
I do have reservations though, I think the foam board will be prone to hold moisture against your sub-floor, giving a place for black mold, termites and rot. I think you could put fiberglass batts in with the "push-wires" and then cover the bottom of the joists with hardware cloth (a wire screen with 1/4" spacing) to allow free flow of air. Let us know how it turns out and maybe post some pictures of your project.
Glenn

The underside of the house is all sand and vented all the way around. I was thinking of sealing the underside of the plywood with a moisture and termite preventative I have seen sold at Ace Hardware before I secure it to the floor joists. Right now, I have the plywood just laying on the tops of the joists. I was thinking of nailing in some 1x2" pressure treated furring strips 2" down from the tops of the joists to lay the cut foam on, then seal any cracks or gaps with a compatible sealant or caulk from the top while it is open and easy to access. Then, screw down my plywood floor, possibly using a construction adhesive along the tops of the joists to make it even more secure.

For a little background on my project... I was going to "sister in" some additional joists to sure up the termite damaged ones, but decided it was just as easy to tear them out and start with all new PT beams. Essentially, I have a complete new foundation sitting on the piers.

Here in Florida.. the rodents have a field day with the batt insulation as was evident in the house where they totally dismantled my AC duct work for nesting purposes. Termites are no problem as I am experienced with them, their signs of intrusion, and a means of irradicating them... but prevention is half the job in fighting them.

Any further comments or advice is very much appreciated. I have some pictures of the project that will soon be posted on my web site. When they are up, I will add the link.